The present invention relates generally to insulated sheathing for use in building construction or the like and, more particularly, to an insulated sheathing having enhanced structural properties.
In constructing a building, and in particular a house, a relatively thin panel board of is commonly used to cover the structural framework of exterior walls. The board is typically fabricated from a low-cost, lightweight material having enhanced insulating properties, such as for example polystyrene or polyurethane foam. Usually, the boards are sized for use in conjunction with conventional frame sections (that is, frames with wooden studs on 16 inch (40.64 cm) or 24 inch (60.96 cm) centers). The boards may also have varying thicknesses and compositions, depending on, among other considerations, the desired resistance to heat flow. In the case of foams, additional layers of materials, called xe2x80x9cfacings,xe2x80x9d are also commonly laminated on or affixed to one or more of the surfaces to create a vapor barrier, increase the stiffness, durability, or resistance, as well as to possibly prevent the release of blowing agents.
While insulating boards fabricated solely of foam or the like provide the desired thermal insulation value, they simply do not have sufficient strength to resist the various wind and other racking type loads created in a typical building. For example, when secured to the frame using typical mechanical fasteners, such as nails or staples, the insulating material is unable to withstand the local tensile and compressive stresses created as the result of in-plane shear forces acting on the frame. The fasteners may tear the insulating panel. As a result, the loads are not controlled and the building integrity is compromised. To prevent this, a common practice is to install metal or wood braces on the boards to handle these loads. However, this increases the overall construction cost and effort required.
Another common practice is to attach a layer of plywood or oriented strand board (OSB) to the frame to provide the desired structural enhancement. However, neither plywood nor OSB provides the desired degree of resistance to heat loss. To maintain thermal integrity with this practice, a layer of insulation board may be placed on the plywood or OSB board. However, this practice significantly increases the overall cost of construction. Also, it increases the wall thickness to the point where special jamb extensions are required to finish out the wall.
In an effort to reduce construction costs without compromising the integrity of the resulting building, others in the past have proposed a reinforced insulating material in the form of a sheathing designed to eliminate the need for adding a separate structural layer, such as plywood, to the frame. For example, U.S. Pat. No. 5,345,738 to Dimakis discloses a structurally enhanced sheathing comprised of a layer of insulating foam in combination with opposing facing layers of a treated cellulosic (paper) material. While this composite sheathing is somewhat stronger than the foam insulation alone, there are shortcomings. First of all, the outer layers are essentially formed of paper, and thus may not provide the desired level of moisture imperviousness and strength. Additionally, forming and laminating facings comprised of several distinct layers add to the manufacturing expense. Of course, cost is a key consideration in the design of structural sheathing, since the builder is trying to keep costs as low as possible to not only increase profits, but also to remain competitive in the market.
Accordingly, a need is identified for an improved sheathing for use in insulating and strengthening a building or the like. The sheathing should be sufficiently strong to avoid the past need for attaching additional layers of wood or the like to the frame to provide at least a minimum level of structural enhancement. The sheathing should also be easy to manufacture at a relatively low cost, such that it results in a significant advance in terms of structural performance per unit cost as compared to prior art proposals.
A structurally enhanced sheathing for use in insulating a building or the like is disclosed. The structural enhancement comes from the use of a structural layer of material in conjunction with an insulating layer of material. The structural material may comprise a plurality of fibers extending in first and second biased directions, and thus, defining a grid having a plurality of openings. The openings are capable of receiving an adhesive for attaching the sheathing to a stable mounting structure, such as a wall frame. Preferably, the fibers forming the structural material are biased relative to a common axis, such as a centerline of the insulating material. Alternatively the structural material may be formed of a polymer film. Preferably the polymer film is a multilayer film adding sufficient mechanical properties to the insulating layer.
In accordance with a first aspect of the present invention, a sheathing for insulating and structurally enhancing a stable mounting structure is provided. The sheathing comprises a first layer of insulating material and a second layer of structural material attached to the insulating material. The structural material includes a plurality of fibers extending in first and second biased directions such that the fibers form a grid having a plurality of openings for receiving a first adhesive for securing the sheathing to the stable mounting structure.
In one embodiment, the insulating material may be selected from the group consisting of extruded polystyrene foam, expanded polystyrene foam, polyurethane foam, polypropylene foam, polyisocyanate foam, polyisocyanurate foam, and combinations thereof. However, it is also possible to form the insulating material of wood, paper, waxed cardboard, and combinations thereof. The insulating material is usually in the form of a rectangular board, but can be of any shape, such as a square, circle, or the like.
To enhance the ability of the structural material to withstand tensile stresses acting on the wall frame to which the sheathing is attached, the fibers may be oriented at any included angle between 0 and 90 degrees. Preferably, the fibers are oriented at first and second biased directions at an included angle of substantially 30 to 60 degrees relative to a common axis, such as a centerline of the insulating material (preferably the longest centerline, such that in the case of a rectangular sheathing, the fibers span from the top corner at one side to the opposite, bottom corner). Double-biasing the fibers at a 45-degree angle relative to a common axis, such as the centerline, is preferred for the majority of building applications. However, the angles of each direction may be different (for example, the first direction is 35 degrees and the second direction is 55 degrees), or the fibers extending in the same direction may be oriented at different angles, depending on the particular types of loading encountered or the degree of racking strength required for a particular application.
Each fiber is preferably comprised of a material selected from the group consisting of glass fibers, polymer fibers, carbon fibers, natural fibers, mineral fibers, metals, polymer films or tapes, or combinations thereof. The fibers may be singular or may be divided into a plurality of bundles or strands. In the case of polymers, the fibers may consist of polyester, nylon, polypropylene, poly-paraphenylene terephthalamide, and other low-elongation polymers. Also, it should be appreciated that the fibers in each plurality may be of different types, weights, lengths, or comprised of different materials in order to meet the anticipated racking load resistance requirements. Preferably, the fibers are continuous or elongated, but it is also possible to use random length, non-continuous fibers.
The selected fibers may be interwoven, layered, or stitched at the proper orientation. In any case, to hold the fibers together during the manufacturing process, an appropriate chemical binder, such as polyvinyl acetate (PVA), may be used as a stabilizer. An alternate manner of creating a fabric from the fibers is to weave them together and bind them to a stabilizing layer, such as a polymer film, using an adhesive, such as a hot melt, pressure sensitive adhesive. The opposite side of the stabilizing layer is then attached or adhered to the corresponding surface of the insulation layer such that the openings in the grid defined by the fibers face outwardly, thereby permitting them to contact the frame in the installed position. As should be appreciated, the stabilizing layer may also add to the racking strength of the resulting structural insulating sheathing.
An optional facing may also be provided for attachment to a substantially planar face of the insulating material opposite the face for receiving the structural material. The facing may include a first layer of polyester film, a second layer of polyester scrim, and a third layer of polyester film. A third adhesive may also be provided for attaching the facing to the insulating material. Additional layers may also be added, as necessary, to farther enhance the sheathing, such as in terms of enhancing the bending strength, stiffness, or thermal resistance.
In accordance with a second aspect of the invention, a sheathing for insulating and structurally enhancing a stable mounting structure is disclosed. The sheathing comprises a first layer of insulating material and a second layer of structural material attached to the insulating material. The structural material includes a plurality of fibers extending in first and second biased directions and thus forming a grid. The structural material further includes a stabilizing layer positioned between the fibers and the insulating material. Preferably, the stabilizing layer is a film, and the plurality of fibers are attached to a first side of the film, while and a second side of the film is attached to the insulating material. This stabilizing layer thus not only serves to hold the fibers in the desired orientation prior to, during, or after attachment of the structural layer to the insulating layer, but also may serve to further enhance the strength of the sheathing.
In accordance with a third aspect of the present invention, an assembly for insulating and structurally enhancing a frame of the type used in constructing a building or the like is provided. The assembly includes a multi-layer sheathing including a first layer of insulating material attached to a second layer of structural material. The structural material comprises a plurality of fibers forming a grid having a plurality of openings. An adhesive is also provided for securing the grid to the frame.
The fibers preferably project in first and second biased directions, with the grid thus formed being regular or irregular depending on the relative angles selected. The adhesive is preferably capable of at least partially penetrating into the openings in the grid and at least partially filling any gaps in a corresponding frame member. Alternatively, the adhesive may be an adhesive tape or any other adhesive substance capable of at least partially penetrating into the openings in the structural material and at least partially filling any gaps in a corresponding frame member. In one embodiment, the fibers are comprised of a material selected from the group consisting of glass fibers, polymer fibers, carbon fibers, natural fibers, mineral fibers, metals, polymer films or tapes, or combinations thereof. Also, it is possible to form the structural material from a plurality of chopped fibers.
In accordance with a fourth aspect of the present invention, a method of insulating and structurally enhancing a frame is disclosed. The method comprises providing a multi-layer sheathing including a first layer of insulating material and a second layer of structural material, the structural material including a plurality of fibers defining a grid having a plurality of openings and attaching the sheathing to the frame with the grid exposed and facing the frame. In a preferred embodiment, the attaching step includes providing a foaming adhesive for securing the sheathing to the frame. The foaming adhesive may be a quick-curing adhesive placed on the frame at the construction site (or the cure time may be altered to suit the factory environment), and a plurality of mechanical fasteners or clamps may be used to hold the sheathing in place on the frame while the adhesive cures. The plurality of fibers are preferably double biased at an included angle of 45 degrees relative to a common axis, such as the centerline of the sheathing, and the method includes orienting the structural insulated sheathing prior to application. In the case of a rectangular sheathing, the orientation is such that the fibers extend in a diagonal fashion, essentially from adjacent to a top corner to adjacent to the opposite bottom corner. Upon application to the frame, this orientation ensures that the desired resistance to shear loading is created.
In accordance with a fifth aspect of the present invention, a method of manufacturing a structurally enhanced, insulated sheathing, is disclosed. The method comprises providing a first layer of a structural material including a plurality of fibers defining a grid having a plurality of openings and a stabilizing layer for holding the fibers in place. The stabilizing layer not only serves to hold the fibers in the desired orientation prior to, during, or after attachment of the structural layer to the insulating layer, but also may serve to further enhance the strength of the sheathing.
In accordance with a fifth aspect of the present invention, a sheathing for insulating and structurally enhancing a stable mounting structure is provided. The sheathing comprises a first layer of insulating material and a second layer of structural material attached to the insulating material. The structural material includes a multiplayer film of PE, EVA and PET. In a preffered embodiment the film incorporates a tri-layer extruded film (LLDPE/LLDPE/EVA) which is glued to a second film (PET). The composite film is then heat sealed to both sides of an extruded polystyrene insulation panel using an in-line hot roll lamination process.